1. Field of the Invention
This disclosure relates to a system for handling samples, and in particular, this disclosure relates to a polar coordinate positioning system.
2. Background of Prior Art
Test tubes and sample cups, also referred to as sample tubes, have long been the method of choice in handling samples. The use of various shaped racks to hold multiple sample tubes has helped in the automation of sample preparation and analysis. Many devices move sample tube racks from a load point to the sampling position or move the sample racks from station to station where sample loading, sampling or reagent addition takes place.
The microplate, also referred to as a microtiter plate or multiwell plate, has become an integral tool used in biology, cellular research, drug discovery research, and a host of other applications, and it is particularly useful in high throughput screening assays. It has allowed automation of many of the steps required for sample preparation and analysis. The geometry of the microplate well arrays have a layout of rows and columns. The 96 well plate, for example, has twelve rows and eight columns. This geometry naturally lends itself to the use of robots that are actuated in a Cartesian coordinate system (x, y). One or more of the sample wells in the plate is positioned to the correct location in an x-y plane where reagents are added to the well or wells, or sample is removed from the well or wells for analysis, by a single or multi-head sampling station.
The X and Y axis motions are usually controlled by motors that are coupled to the microplate holder by some combination of gears, belts, pulleys, cables, or lead screws in combination with a rail-bearing system to control the motion in each axis. The motors are used in combination with an open loop or closed loop control system. A series of switches, sensors, or encoders are used to define the zero point of the positioning and keep track of the location relative to the zero point. Some systems use linear actuators to position, thereby combining the rail-bearing and motor in a single unit.